In the past various methods have been used to provide materials that are capable of filling as much of the annular space between production tubing and a wellbore wall as possible, in both cased and open hole wellbores. Two particular situations have required specialized materials or structures for this purpose. These situations include sand control and isolation of a portion of the formation.
Sand control, in particular, has been a problem addressed by many inventions. In general, sand control methods have been dominated by the use of gravel packing outside of downhole screens. The goal is to fill the annular space outside of the screen with sand which will operate to prevent the production of undesirable solids from the formation, while still allowing flow of desirable production fluids. More recently, with the advent of tubular expansion technology, it has been thought that the need for gravel packing might be eliminated if the screen or screens could be expanded in place to eliminate the surrounding annular space that had heretofore been packed with sand. However, problems have been encountered with the screen expansion technique because of wellbore shape irregularities. While a fixed swage can be used to expand a screen by a fixed amount, it does not effectively address the problem of wellbore irregularities. Furthermore, a washout in the wellbore can result in formation of a large annular space outside of the screen, while an area of unanticipatedly small diameter in the wellbore can result in sticking of the fixed swage, causing problems in getting the fixed swage to the desired location.
One improvement over the fixed swage is the flexible swage, for which various designs exist. These swages flex inwardly in tight areas, which may reduce the chance of sticking. Unfortunately, flexible swages still have a finite expansion capability, and therefore the problem of annular gaps or voids beyond the range of the swage remains unaddressed.
Alternative screen designs have included use of a pre-compressed mat held by a metal sheath, that is then subjected to chemical attack when placed in a desired downhole location. Once in position the mat is allowed to expand from its pre-compressed state, but the screen itself does not expand. Examples of this design and other alternatives are described in, for example, U.S. Pat. Nos. 2,981,332; 2,981,333; 5,667,011; 5,901,789; 6,012,522; 6,253,850; 6,263,966; 5,833,001; and 7,013,979 B2. Unfortunately, many of these designs suffer from the problem of relatively rapid “locking in” of the space-filling means at a given location following its introduction downhole. This rapid “lock-in” in many instances prevents or discourages the repositioning of the device for optimum performance, and frequently requires costly remediation efforts to ensure the goals of the device are adequately met.
Thus, what is needed in the art is a means and method of enabling filling of an annular downhole space in a way that reduces the incidence of unfilled voids and that ensures that goals such as, for example, sand control or annular isolation, can be accomplished. It is also desirable that such means and method offer improved flexibility in positioning or repositioning a space-filling means within an acceptable time period.